參考博文：

http://www.xuanyusong.com/archives/1878

http://blog.csdn.net/muyu114/article/details/12968067

總結如下：

UIViewController* ctrol;

if ( [[UIDevice currentDevice].systemVersion floatValue] < 6.0)
    {
        // warning: addSubView doesn't work on iOS6
        NSArray* array=[[UIApplication sharedApplication]windows];
        UIWindow* win=[array objectAtIndex:0];
        
        UIView* ui=[[win subviews] objectAtIndex:0];
       ctrol =(UIViewController*)[ui nextResponder];
    }
    else
    {
        // use this method on ios6
      ctrol=[UIApplication sharedApplication].keyWindow.rootViewController];
    }

接入銀聯sdk所遇到的問題，需要傳入 viewcontroller,此時傳入ctrol即可